Immediate and future radiation from the Fukushima Daiichi nuclear disaster may result in hundreds of deaths and emerging cancer cases, according to a yearlong modeling project undertaken by researchers at Stanford University.

Started within a week of the Fukushima meltdown, the project is the most detailed model yet of the emission, transport and deposition of radioactive material from the site, accounting for complex interactions between atmospheric conditions and the microphysics of radioactive particles.

Combining the projected spread of radioactive material with a standard radiation health-effects model, co-authors John Hoeve, a recent Stanford Ph.D. graduate, and civil engineering professor Mark Jacobson calculated that between 15 and 1,300 premature deaths would occur as a result of the accident.

Within that wide range, the team poses a best guess of 130 direct deaths resulting from radiation inhalation and exposure.

Those findings contest the hypothesis, circulated among some experts in the aftermath of the accident, that radioactive fallout from the Fukushima disaster would not result in any long-term human mortality.

Some mixed blessings
The full meltdown of Fukushima Daiichi reactor Units 1, 2 and 3 constituted the most serious nuclear event since the 1986 Chernobyl disaster in Ukraine, creating a contaminated "dead zone" of several hundred square kilometers and resulting in the evacuation of hundreds of thousands of people.

Yet the Fukushima disaster differed from Chernobyl in several important ways, according to the researchers. Nearly 80 percent of the radioactive material from the Japanese event ended up in the ocean, to be diluted by ocean currents, while the vast majority of Chernobyl's fallout ended up in Russia and Belarus and other neighboring states.

Fukushima's radioactive release was also limited by more stringent safety measures and a quicker response time, the report notes.

The remaining 20 percent of leaked radioactive material traveled through the air, moving with atmospheric currents, until it was eventually deposited on land. While the vast majority of grounded radioactive material has been detected in Japan, smaller traces have been detected as far away as North America and Europe.

"As you move away from Japan, you get an exponential decrease in radioactivity concentration," said Jacobson.

In the case of Fukushima, no deaths have yet been identified as the direct result of radiation exposure. But according to Jacobson, those effects can take years, even decades, to manifest.

"We know that there were 600 deaths that resulted from the evacuation," due primarily to stress and fatigue, he said. "There were also between 10 and 12 worker fatalities at the Fukushima plants. Our estimate looks at the expected deaths over a lifetime of exposure to low levels of radiation."

Simulating particle physics on a global scale
While the effects of radiation are highly variable, he said, exposure is particularly dangerous for children, for whom any exposure constitutes a proportionally larger concentration of radioactive material.

The model shows that a failure to evacuate the area immediately surrounding the Fukushima power plant would have resulted in, at most, an extra 245 radiation-induced deaths.

Considering that about 600 deaths are currently attributed to the evacuation process itself, it is possible that the government's security measures cost more lives than they saved, Jacobson said.

In the months preceding the Fukushima disaster, Jacobson, whose work focuses on chemical transportation, had been preparing computer programs to model pollution movement from Asia to the United States. When disaster struck on March 11, 2011, he realized his opportunity to put his models to work.

Adjusting his programs to accommodate radionuclide data and emissions data from Japan, Jacobson and Hoeve began running their simulations shortly after the meltdown.

So complex were the models -- which account for atmospheric and oceanic circulation, as well as the processes of dissolution, coagulation and decay that characterize aerosol particles -- that they required the computing power of supercomputer clusters at both NASA and Stanford University.

Even so, each simulation required four to six months to run, said Jacobson.